oil

[grantll]

If 10w 30 or other such oil changes to heaver weight why does the oil pressure drop when engine warms up

 

[SVcummins]

This one will be interesting? I send oil analysis samples in for my equipment and part of the test is they use a viscometer to test the weight or viscosity of the oil at a certain temp and it usually always test 40 on 15 40 weight oil

 

[Crazy Horse]

Interesting question ........ I'm not sure that multi-grade oil necessarily "thickens" when it gets warmer. I think the concept of say a multigrade 10W30 oil is that it has the lubricating properties of a 30 weight oil when it reaches operating temperatures. Remember that even straight 30 weight oil for example will "thin out" a bit when warm as compared to what it's like before starting up your engine. I might be wrong on all of this, I'm just telling my understanding of what it means and how it works.

 

[grantll]

So it does not change weight but does visosity

 

[Keith-OR]

The w does not stand for weight..

The first viscosity number is the ?winter? number, hence the ?w? after it. This number is tested at 0?F. The second number is tested at 212?F to simulate the heat of an engine at operating temperatures. That means a 10w30 oil takes 10 seconds to flow through the tube when cold, and 30 seconds when hot.

Normally, fluids thin as they warm up and thicken as they cool, but these oils have additives that cause the opposite to happen.

 

[grantll]

Please don't think L am trying to be smart if your last statement is the way it works why does the oil pressure drop?

 

[Geo-TH,In]

I try not to overthink oils too much. I just use what the manufacturer recommends.

I have noticed some newer cars recommending a 5w30, some a 5w20.

I think is colder climates a 0w20.

I recently noticed on a newer Terramite they have changed to a 15w40 for summer, where in past they wanted a 10w40 and A BIG WARNING: NEVER USE HYDRAULIC OIL.
Now in the winter you can use 10w Hydraulic oil.

Go figure. Way above my level of comprehension.

 

[Steve@Advance]

I think the simple answer is multi grade oil doesn't thicken up "as bad" when cold as straight weight oil.

There is still thinning when heated, and it probably gets a little thinner than straight weight oil when hot.

One thing to think about, everybody worries when they see low oil pressure on a well worn engine when it's idling. As long as it has "some" oil pressure, and no new unusual noises, or sudden drop in oil pressure, the oil is still circulating and getting where it needs to go.

What is not seen is oil not getting where it needs to go when it's cold. The gauge may read high, even exceptionally high, oil filter blowing high! But at the same time there is a tiny restrictor orifice or a metered oil flow up 2 feet of cold oil galley above the oil pump that is not moving oil because it's so cold and thick! Meanwhile the poor rocker arm assembly is screaming for the oil that ran down when it was shut off hot!

That is where multi grade oil comes to the rescue. Better to loose some warm oil pressure than no oil to the extremities when cold!

 

[Keith-OR]

A lot depends on what clearances are in the oil pump, cam, rod and main bearings. also when ya put the oil in it is not at the operating temp the oil is rated at, as the engine warms up to operating temp,oil will obtain the viscosity of 30 weight, therefore the oil pump is not pumping higher viscosity cooler oil. So all depends on how many hrs or miles is on the engine and how wore out it is, clearances on all moving parts.

Here is a suggestion from oil munfacrures:
The manufacturer?s oil recommendations should be followed for the life of the engine; instead of using thicker oil when the motor starts to burn or leak oil, switch to a high mileage formulation. These oils address these issues with added conditioners that can help restore internal seals.

 

[Crazy Horse]

Keith ..... you're right about the W letter ..... and actually I did know that the W stands for winter. I don't see where I said it means weight in my post, maybe you were referring to someone else or assuming I said that? Thickening and thinning, not sure if those are correct terms to use although for guys like you and me, they seem to make sense and are easy to comprehend. Your last statement (as stated) is questionable I think. Not sure where you live but every winter I see our winter oil up here, say 5W30 which is a common one, at -25 degrees and it doesn't seem to have a lot of flow properties, it actually appears to be pretty "thick" (more viscous is the proper term I think with viscosity being resistance to flow) when it's that cold. Once it's in the engine and warmed up though, it is considerably less viscous (appears "thinner" and it has less resistance to flow) so really, it doesn't actually thicken up once it's hot, once again the use of those terms is misleading I think. Some of this scientific explanation below in the link requires some careful reading to get everything straight.
Untitled URL Link

 

[SVcummins]

Viscosity and weight mean the same thing . The oil is 40 weight at whatever temperature they test it at I can?t remember the temperature but as posted they do the test at a temperature that a hot engine would be

 

[ss55]

It is easiest to understand if you look at a graph of viscosity verses temperature curves.

 

[Brendon-KS]

Your last sentence isn't quite accurate - all oil will become less viscous (in other words "thin out") when heated. What happens with a multi-viscosity mineral oil is that the polymer chains it contains will lengthen when heated and prevent as much thinning as you would get otherwise with a single-viscosity oil. When cold these polymer chains are constricted so the oil acts like the "W number" on the label. If I understand it right the mechanisms with synthetic oil are different and they achieve the same effect without utilizing polymer chains. This would be beneficial because over time these chains can become broken down due to shearing action and the mineral oil will gradually loose some of the "remain thick" properties that they provide.

 

[Keith-OR]

this statement came directly from automotive engineer site.

 

[Brendon-KS]

If this were true than multi-viscosity oil would pour out of the bottle faster and more completely if you put it in the freezer for a few hours first compared to setting the bottle in the hot sun. From experience we all know this is not the case. Every chart out there that relates any kind oil's viscosity with temperature shows a decreasing viscosity with increasing temperature. The multi-viscosity oil line will, however, have less slope than a single-viscosity oil which means they provide acceptable viscosity over a wider temperature range.

 

[rustred]

because your engine brgs are worn. and the pump cant keep up the supply because its disappearing due to larger brg. clearances. no othe reason.

 

[Keith-OR]

If ya have a problem with eng. findings go tell them about it.!!!!

 

[tlock0331]

(quoted from post at 20:18:49 08/08/18) because your engine brgs are worn. and the pump cant keep up the supply because its disappearing due to larger brg. clearances. no othe reason.

ill second that, i usually find the cam bearings are shot....and so far, ive been 4 for 4 on that....

 

[IanC]

Asking an automotive engineer about oils is like asking your urologist about the best way to pull a tooth. Both smart in their OWN field. https://www.api.org/

 

[buickanddeere]

What machine are you operating ?